Temperature-controlled corrosion test probe



July 27, 1965 sc sc ETAL 3,197,698

TEMPERATURE-CONTROLLED CORROSION TEST PROBE Filed Dec. 7, 1959 TEMP TURE OONTR GORROSIVE [78 [8o /ATMO5PHERE\ 30 22 g gmm REFERENCE 58 52 SPEOIMAN 64 54 53 74 68 56 1 w @Q Y I l y ROBE ATTO RNE Y 3,197,698 TEMPERATURE-CONTROLLED CURROSIGN TEST PRUBE Edward Schaschl and Robert L. Littler, Crystal Lake, 111., assignors to The Pure Gil Company, Chicago, Iih, a

corporation of Ohio Filed Dec. 7, 1959, Ser. No. 857,368 4 Claims. (Cl. 32465) This invention relates to a temperature-controlled corrosion-test probe and, more particularly, to a corrosiontest probe for use in investigating corrosion phenomena related to the metal walls of heating or cooling equipment.

In many instances it is desirable to deter-mine the corrosion rates of metals in equipment where wall temperatures are significantly different from bulk fluid temperatures, such as in heat exchangers, furnace flues, valve rocker-arm chambers of engines, etc. In these instances, the difference between the temperature of the metal and the temperature of the gas or liquid in contact with it can affect the rate of corrosive attack. For example, in the flues of furnaces or in the valve rocker-arm chambers of engines, the metal walls, cooled by air or water, cause condensation of corrosive constituents on the interior metal surface. Then to, the metal walls of the tubes and shell in a heat exchanger may be hotter or colder than the bulk temperature of the liquid or gas in contact with them, and this can greatly aggravate corrosion. As an example, phosphorus pentasulfide can be cooled by stainless steel without rapid corrosion of the stainless steel, but heating the phosphorus pentasulfide through the stainless steel causes very rapid attack of the metal. It is apparent that conventional corrosion-test probes, which are merely inserted into the environment under study and attain the temperature of the fluid, cannot be used to precisely determine the corrosion rate under such conditions.

The instant invention relates to a temperature-controlled corrosion-test probe providing means whereby conditions of corrosion can be duplicated, wherein the metal wall or member under study can be either a cooling or a heating surface, thus permitting realistic determinations of corrosion rates. The probe of this invention utilizes a heating or cooling medium which is passed through a chamber housing corrosion-test elements which are made of the material of construction under study. The thermal conditions within the chamber are adjusted to duplicate various combinations of conditions which the material of construction experiences when utilized as the body of a heat exchanger, furnace flue, or wall of a valve rocker-arm chamber, etc. The device of this invention is designed to permit corrosion-rate studies under actual conditions existing in practice.

It becomes therefore a primary object of this invention to provide a thermally-controlled corrosion-test probe.

Another object of this invention is to provide a corrosion-test probe for use in investigating corrosion phenomena related to the metal walls of heating or cooling equipment.

Another object of this invention is to provide a corrosion-test probe adapted to duplicate the temperature conditions or fluctuations associated with a material of construction or part thereof while simultaneously subjecting the material of construction to a corrosive atmosphere.

These and further objects of this invention will become apparent or be described as the specification proceeds.

The invention is best understood by reference to the drawings wherein:

FIGURE 1 is a perspective view of the device of this invention;

United States Patent ice FIGURE 2 is a cross-sectional view taken along lines 2-2 in FIGURE 1, also showing the mode of attachment of the device to the Wall of a vessel indicated at 78;

FIGURE 3 is a cross-sectional view taken along lines 3-3 in FIGURE 1. i

In the drawings, numeral 16 refers to a housing which is shown as a rectangular member having end walls 12 and 14, bottom 16, and sides 18 and 20. Housing 10 has an open top and an inside chamber 22. End 12 has conduit 24 extending through in communication with chamber 22. Similarly, conduit 26 extends through the opposite end 14 into communication with chamber 22. Housing 10 has a circumferential flange 28 with bolt holes 30 extending at spaced intervals therethrough. The inner edge 32 of flange 28 provides a recess to receive retainer member 34 held in place by stud bolts 36 which extend into threaded holes in the wall of housing 10. Retainer member 34 is provided with an opening 38. Gasket 40 fits between the underneath side of retainer member 34, adjacent to and around opening 38, to provide a seal for first test specimen 42 which forms the top wall of chamber 22. Opening 38 in the retainer member 34 allows the corrosive atmosphere to contact the outer side of test specimen 42.

The bottom 16 of housing 10 has aperture 44 leading to external electrical conduit 46 to provide means for attaching the lead wires within the test probe. For this purpose, an electrical terminal or conductor 48 is provided against the inside of wall 12. The top edge 50 of terminal or conductor 48 makes electrical contact with the test specimen 42. Lead wires 52 and 53 are soldered at 54, or otherwise connected to base 56 of terminal 43. An aperture 58 is provided to match the conduit 24 to provide open communication therethrough.

A similar arrangement is provided for the remaining members of the test probe located Within chamber 22, whereby terminal 60 makes contact at 62 with the other end of test specimen 42, aperture 64 is opposite conduit 26, and lead wire 66 is soldered to base 68. The second or reference test specimen to complete the probe is provided at 70, same being soldered or otherwise fastened to base 68 of terminal 60 at 72. Lead Wires 74 and 76 are attached to the opposite end of reference test specimen 7ti. Preferably, contact areas 50, 62 and 72 are soldered connections. Conduits 24 and 26 provide inlet and outlet ports for the temperature control medium which is passed through chamber 22 in contact with both test specimens.

By the foregoing arrangement of test specimens and lead wires, the test probe is adapted to be connected to a corrosion meter or other suitable resistance-change-measuring instrument. In one mode of operation wherein test specimen 42 is the corroding element and test specimen 7! is protected from corrosion, the lead wires are connected so that the test specimens become resistances in opposite arms of a Wheatstone bridge circuit, and terminal 60 with lead 66 becomes the common junction. Since both test specimens 42 and are at the same temperature and specimen 70 does not corrode, the device incorporates the temperature-compensating features that are desired in instruments of this type. No novelty or invention is alleged in the foregoing electrical arrangement wherein one element is exposed to the corrosive atmosphere, the other protected element is subjected to the same thermal conditions, and the rate of corrosion is measured by following the change in resistance of the exposed element due to its decrease in cross-sectional area by means of a resistance-change-measuring circuit. The present invention is directed to the arrangement of apparatus elements disclosed herein, and particularly the provision of means such as chamber 22 in contact with both test specimens,

Patented July 27, 1965 is whereby the thermal conditions influencing the test-probe assembly can be varied to duplicate various corrosion problems.

The present device is adapted to be attached to a separate vessel, the wall of which is shown at '73, confining the corrosive atmosphere, whereby the outer surface of test specimen 42 is exposed to the corrosive atmosphere therein. This is accomplished by means of attaching bolts or studs through holes 30 in flange 2 8 and through matching'holes S in the periphery of the opening in vessel wall 73. In one embodiment of this invention, the test probe is adapted to be attached over an opening in the oil pan of an internal combustion engine whereby studies can be made of the corrosion rate of test specimen 42 in contact with the lubricating oil therein.

Methods have been devised which make use of the correlation between change in electrical conductivity and change in cross-sectional area to determine the rate of corrosion of materials of construction in a corrosive atmosphere through the use of corrosion-test probes connected to electronic resistance-change meters. These instruments, employing resistance bridges, function like analogue computers to indicate quantitatively those changes in physical characteristics which cannot be conveniently measured by other methods. One application of such a bridge is described in a co-pending application entitled Apparatus for Determining the Influence of Corrosion on Metallic Materials of Construction, bearing Serial Number 528,032, filed August 12, 1955, by G. A. Marsh and E. Schaschl which relates to means for compensating for temperature changes. In this apparatus, one of the coupons or test specimens in the probe is insulated from the corrosive environment by means of a suitable protective coating. The coupons in the probe are connected so .as to comprise one-half of a typical resistance bridge. Suitable electrical conection-s are made with the other half of the bridge, which is placed outside the corrosive environment along with the power supply to the bridge, and an appropriate electrical meter, such as a galvanometer, functions as a null detector. Loss of metal on the unprotected specimen induces small increases in resistance in the circuit which are correlated with metal loss by appropriate formulae described in the application.

In another copending application entitled Electronic Resistance-Change Meter, Serial Number 528,061, filed August 12, 1955, now United States Patent No. 2,830,265, by Lynn E. Ellison there is described an electronic apparatus for conveniently detecting and measuring changes in resistance and provides for the direct reading of the rate of corrosion. The corrosion-test probe of the present invention may be used in conjunction with the apparatus described in the foregoing applications.

The first and second test specimens 42 and 70 have substantially the same resistivity, and may have substantially the same chemical composition. This is necessary in order that the bridge-measuring circuit can be made to function accurately without tedious calibration. However, it is unnecessary that the configuration or total resistance of protected and unprotected test specimens be identical, because the corrosion-measuring process with which the test probe of this invention is used utilizes a comparison method for determining the change in resistance of the unprotected test specimen or resistance element when exposed to corrosive conditions. The bridge circuit in which the test probe is installed during use is initially balanced by adjusting the ratio of the resistance elements.

Accordingly, although test specimens 42 and 70 are shown as rectangular-formed pieces, they may be in the form of elongated sheets or strips and have other shapes than shown.

Advantages occur in constructing the metal corrosiontest elements 42 and 70 so that they have substantially the same resistance values. However, suitable unsymmetrical corrosion-test elements can be used in which the resistances are not identical, provided, for the sake of consistency, a material of construction is employed which is of substantially uniform composition. The ratio of the resistance of the unprotected test specimen to the resistance of the protected test specimen may vary from values of about 0.1 to 10. The use of test specimens having different resistances within these ratios requires that corresponding changes in the values of the resistances of the other branches in the bridge circuit be made. Gther factors must also be considered in the design of a suitable corrosion-testing unit or probe. Lead wire resistance, for example, will be appreciable if a small corrosion-testing probe is used in which the resistance of one element is only about one-tenth or less of the resistance of the other element. Lead wire resistance can be substantially eliminated by the manner of interconnectin g the corrosion testing unit with the bridge circuit.

The wall thickness of the test specimens 42 and 70 may vary from about 0.1 to 0.03 inch and even as small as 0.001 inch depending upon the type of material of construction used and the type of corrosive environment to be studied. The presence of the temperature-controlling medium in chamber 22 prevents rupturing of test specimen 42 where relatively thin specimens are used. The device can be designed by the proper use of materials forming the housing 10 to withstand pressures as high as 2500 p.s.i.g. and temperatures over 1000 F. The gasket member 40 is made from any electrically insulating, chemically inert material, such as Teflon (a proprietary product comprising polytetrafluoro ethylene), plastic, rubber or fiber. Specimen 70 may be coated, if necessary, to protect it from the temperature-controlling medium.

The housing 10 is preferably constructed of a non-conducting material to avoid the necessity of insulating terminals 43 and and test specimen from the housing. For this purpose, such non-corrodible electrical insulating materials as XXPhenolic, XXPPhenolic, XXXPhenolic, XXXPPheuolic (proprietary products comprising phenol-formaldehyde resins) (phenol-formaldehyde resins) and epoxy resin laminates may be used. Where high temperatures are contemplated, such materials as glass fiber laminates, including melamine having a maximum operating temperature of about 260 F., silicone, Teflon, and ceramic insulators, such as titanite, steatite and glass-bonded mica may be used where the operating temperatures may vary from 300 to as high as 750 F. without deleterious effect upon the housing. These materials, described in Materials and Methods, volume 42, No. 1, July 1955, exhibit good metal-bonding strength, flexing strength, and arc resistance and are of low cost.

In fabricating the test probes and test elements of this invention, care should be taken not to have dissimilar metals or conductive materials exposed to the corrosive atmosphere at adjacent portions of the apparatus where one of the exposed portions is the metal surface or material under test, because galvanic effects occur which lead to errors in the corrosion-rate determinations. The test elements 42 and 70 are composed of the metal or metal alloy which corresponds to the material of construction, the corrosion properties of which are to be determined. The materials of construction include all metal and metal alloys such as steel, iron, bronze, brass, copper and the like.

The corrosive atmosphere may be liquid phase, gaseous phase, or mixed phase or may contain suspended solids, as in the fluid cracking system wherein particulate solid particles of catalyst are suspended in a hot mixture of hydrocarbons. The probe of this invention is applicable to the study of corrosion or erosion in any type of atmosphere which causes the disintegration of the confining vessel. Examples of corrosive or erosive atmospheres are acid solutions, brine solutions, drilling muds, alkaline solutions, acidic gases, ammonia, sulfur vapors, hydrogen sulfide, hydrochloric acid, hydrofluoric acid, air, moist air, steam and powdered solids. Examples of temperature-controlling media include water, steam, refrigerants, inert gases, Dowtherm (diphenyl, diphenyl oxide mixture), and the like.

Corrosion per se is generally associated with ferrous materials of construction although both corrosion, that is chemical disintegration, and erosion, or mechanical disintegration, constitute problems with materials of construction containing iron. The device of this invention applies to studies of both erosion and corrosion, i.e., both types of disintegration, particularly as found in connection with ferrous materials of construction.

Having thus described the invention which is not to be limited by the specific embodiments described herein, the only limitations attaching thereto appear in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a corrosion-testing device the combination of a fluid-tight housing having side Walls, bottom, end walls and an open top, said side and end walls terminating in a peripheral planar surface, a first test specimen attached across said open top in sealed relationship with said peripheral planar surface to form a chamber within said housing, a second test specimen within said chamber and spaced from said first test specimen, a pair of electrical conductors connected to spaced points along said first test specimen, one of said conductors beig connected to said second test specimen and inlet and outlet conduit means in fluid communication with said chamber.

2. A corrosion-testing device in accordance with claim 1 in which said peripheral planar surface has inner and outer edges, each of said electrical conductors extends contiguous with an end wall of said housing and terminates coincident with the inner edge of said planar surface, said first test specimen is in sealed relationship with the inner edge of said planar surface and contacts the termini of said conductors, a circumferential flange around the outer edge of said planar surface adapted to be attached in sealed relationship over an aperture of a vessel containing a corrosive atmosphere.

3. In a corrosion-testing device the combination of an elongated housing having side walls, bottom, end walls and an open top, a peripheral inner recess around said Open top, a first flat metallic test specimen attached in sealed relationship within said recess so that the outer side of said first test specimen is exposable to an atmosphere outside said housing and the inner side thereof defines a wall enclosing a chamber within said housing, a second flat metallic test specimen attached to the inner side of the bottom of said chamber with the ends thereof spaced from the end walls of said chamber, a first L- shaped fiat electrical conductor having one leg thereof in contact with the inner side and at one end of said first test specimen and extending in juxtaposition with the inner side of one end wall of said chamber and the other leg thereof extending in juxtaposition with the inner side of said bottom into contact with one end of said second test specimen, a second L-shaped fiat electrical conductor having one leg thereof in contact with the inner side and at the remaining end of said first test specimen and extending in juxtaposition with the inner side of the remaining end wall and the other leg thereof extending in juxtaposition with the inner side of said bottom and spaced from the remaining end of said second test specimen, a flange around said recess for attachment of said housing across an opening of a vessel confining a corrosive atmosphere, inlet and outlet conduit means in communication with said chamber, an aperture through said bottom Within the space between the leg of said second conductor and the remaining end of said second test specimen, and electrical leads in sealed relationship within said aperture connecting to said conductors and to the remaining end of said second test specimen.

4. In a corrosion-testing device the combination of an elongated rectangular housing having side Walls, bottom, end walls and an open top, a peripheral inner recess around said open top, a gasket seal Within said recess, a first flat metallic test specimen against said gasket seal over said openingto enclose a chamber within said housing, a second fiat metallic test specimen attached contiguous to the inner side of the bottom of said chamber with the ends thereof spaced from the end walls of said chamber, a first L-shaped fiat electrical conductor having one leg thereof in contact with one end of said first test specimen and extending contiguous to the inner side of one end wall of said chamber and the other leg thereof extending contiguous to the inner side of said bottom into contact with one end of said second test specimen, a second L-shaped fiat electrical conductor having one leg thereof in contact with the remaining end of said first test specimen and extending contiguous with the inner side of the remaining end wall and the other leg thereof extending contiguous with the inner side of said bottom and spaced from the remaining end of said second test specimen, a flange around said recess for attachment of said housing across an opening of a vessel confining a corrosive atmosphere so as to expose the outside of said first test specimen to said corrosive atmosphere, inlet and outlet conduit means in communication through the ends of said housing and through said conductors within said chamber for the passage therethrough of a fluid temperature-controlling medium in contact with the inner sides of said test specimens, and an aperture through the bottom of said housing at the space between said second conductor and said second test specimen for the attachment therethrough of electrical leads.

References Cited by the Examiner UNITED STATES PATENTS 2,264,968 12/41 De Forest 73l5 2,484,736 10/49 Razek 7315 2,551,624 5/51 Moore 73-15 2,702,948 3/55 Seney 324- 2,735,754 2/56 Dravnicks 32465 2,769,334 11/56 Soehngen 7315 2,856,495 10/58 Chittum et a1 32465 2,878,354 3/59 Ellison 324-713 2,957,130 10/60 Dietert et al 32465 OTHER REFERENCES Hudson: The Atmospheric Corrosion of Metals Proc. of the Physical Society, vol. 40, 1927, pp. 107-129.

FREDERICK M. STRADER, Primary Examiner.

SAMUEL BERNSTEIN, WALTER L. CARLSON,

Examiners. 

1. IN A CORROSION-TESTING DEVICE THE COMBINATION OF A FLUID-TIGHT HOUSING HAVING SIDE WALLS, BOTTOM, END WALLS AND AN OPEN TOP, SAID SIDE AND END WALLS TERMINATING IN A PERIPHERAL PLANAR SURFACE, A FIRST TEST SPECIMEN ATTACHED ACROSS SAID OPEN TOP IN SEALED RELATIONSHIP WITH SAID PERIPHERAL PLANAR SURFACE TO FORM A CHAMBER WITHIN SAID HOUSING, A SECOND TEST SPECIMEN WITHIN SAID CHAMBER AND SPACED FROM SAID FIRST TEST SPECIMEN, A APAIR OF ELECTRICAL CONDUCTORS CONNECTED TO SPACED POINTS ALONG SAID FIRST TEST SPECIMEN, ONE OF SAID CONDUCTORS BEIG CONNECTED TO SAID SECOND TEST SPECIMEN AND INLET AND OUTLET CONDUIT MEANS IN FLUIT COMMUNICATION WITH SAID CHAMBER. 